CONICET | Buscador de Institutos y Recursos Humanos

Sediment short cores from Chascomús Lake, a shallow lake in the pampas from Buenos Aires province, Argentina (lat. 35deg 36min S, long. 58deg 00min W), were investigated to reconstruct high-frequency climatic variations for the last 500 years. Our analysis of cores focuses on changes in sedimentological, paleontological, geochemical, and rock-magnetic parameters in order to characterize the physical and chemical paleohydrology and river influence on the lake, and allow for the correlation between cores for lake-level reconstructions. The chronology is constrained to 1486 AD (~ 35 cm). As a working hypothesis, we have extrapolated a constant sedimentation rate since there is no drastic variation in the sediment. By this way, two increases in lake level related with pulses of fluvial input were dated around 1660 AD and 1790 AD.Clastic sediment flux by considering grain size remained minimal during low lake-levels, when Limnocythere-dominated assemblages reflect high alkalinity and groundwater input. Thereafter, Cyprideis-dominated assemblages, decreasing organic carbon levels in lake sediments and sediment and concentration/grain size magnetic parameters indicate the return of fluvial runoff to the lake system, and the presence of diluted, low salinity waters. We compare the timing of these lake level fluctuations with the sunspot numbers, a proxy for solar activity reconstructed by Brand et al. (2000).Low lake levels coincide with intervals of unusually low sun activity, the Maunder and Dalton Solar Minima. This allows us to infer that lake sediments contain valuable paleoclimate information related to high frequency climatic variability in the Argentine pampas.

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